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Abstract:

A fluid condition and level sensor is provided that includes a solenoid
body, a coil, and an armature surrounded by the coil. The solenoid body
defines an armature chamber in which the armature is movable in response
to energizing of the coil. The sensor is mounted to a reservoir such that
a first portion of the solenoid body extends into a cavity defined by the
reservoir, and so that movement of the armature is substantially
transverse to a direction of fluid level change in the reservoir. The
first portion of the solenoid body defines an opening permitting fluid
communication between the cavity and the armature chamber, such that
fluid enters and is displaced from the armature chamber through the
opening as the armature moves, movement of the armature within the
armature chamber thereby being affected by fluid level in the reservoir.

Claims:

1. A fluid condition and level sensor for a fluid-containing reservoir,
comprising:a solenoid body configured for mounting to the reservoir;a
coil connected with the solenoid body;an armature surrounded by the coil;
wherein the solenoid body defines an armature chamber in which the
armature is movable in response to energizing of the coil;a pole
piece;wherein at least a first portion of the solenoid body extends into
a cavity defined by the reservoir when the solenoid body is mounted to
the reservoir;a biasing device biasing the armature away from the pole
piece and toward the first portion of the solenoid body, the biasing
device and coil being configured to cycle the armature in the armature
chamber as the coil is cyclically energized;wherein the first portion of
the solenoid body within the cavity defines an opening permitting fluid
communication between the cavity and the armature chamber, such that
fluid enters and is displaced from the armature chamber through the
opening as the armature moves, such that fluid level within the armature
chamber corresponds with the level of fluid in the reservoir, movement of
the armature within the armature chamber thereby being affected by fluid
level in the reservoir.

2. The oil condition and level sensor of claim 1, wherein the sensor is
mounted so that movement of the armature is substantially transverse to a
direction of fluid level change in the reservoir.

3. The fluid condition and level sensor of claim 1, wherein the opening is
sufficiently spaced from the armature such that fluid flow is permitted
through the first opening during an entire range of motion of the
armature within the armature chamber.

4. The fluid condition and level sensor of claim 1, wherein the solenoid
body and the armature define a clearance permitting fluid in the armature
chamber to move therethrough as the armature moves in the chamber.

5. The fluid condition and level sensor of claim 1, wherein the opening is
a first opening and establishes fluid communication between a first
portion of the armature chamber and the cavity; wherein the solenoid body
defines a second opening permitting fluid communication between the
cavity and a second portion of the armature chamber, the first and second
portions being at opposing sides of the armature, both sides of the
armature thereby being in fluid communication with the reservoir.

6. The fluid condition and level sensor of claim 5, wherein the first
opening is in communication with the reservoir at a higher fluid level
than the second opening when the solenoid body is mounted to the
reservoir.

7. The fluid condition and level sensor of claim 1, wherein the armature
is characterized by an absence of any orifices establishing fluid
communication between the armature chamber and the reservoir.

8. A fluid condition and level sensing system for a fluid-containing
reservoir comprising:a fluid level sensor having a solenoid body
configured for mounting to the reservoir, a coil, an armature, and a pole
piece; wherein the solenoid body defines an armature chamber between the
armature and pole piece; wherein the armature travels in the armature
chamber in response to energizing of the coil;wherein the solenoid body
defines a first opening establishing fluid communication between the
armature chamber and a cavity defined by the reservoir when so
mounted;travel time of the armature within the armature chamber thereby
being affected by fluid level in the reservoir; anda controller
operatively connected to the coil and operable to determine at least one
of fluid temperature, fluid viscosity, and fluid level.

9. The fluid condition and level sensing system of claim 8, wherein the
controller is configured to determine fluid temperature based on
electrical resistance of the coil.

10. The fluid condition and level sensing system of claim 8, wherein the
controller is configured to determine fluid viscosity based on a
comparison of armature travel time with predetermined armature travel
times associated with predetermined viscosity values.

11. The fluid condition and level sensing system of claim 8, wherein the
armature is positioned to travel substantially transverse to fluid level
in the reservoir when the solenoid body is mounted to the reservoir.

12. A fluid condition and level sensor in combination with a
fluid-containing reservoir comprising:a solenoid body;a coil, an
armature, and a pole piece; wherein the solenoid body defines an armature
chamber between the armature and pole piece; wherein the armature travels
in the armature chamber in response to energizing of the coil; wherein
the solenoid body defines a first and a second opening permitting fluid
communication between fluid in the reservoir and the armature chamber at
respective opposing sides of the armature;wherein the openings are
configured to establish positive displacement of fluid through the
chamber and openings as the armature travels and to affect travel time of
the armature in the armature chamber in correspondence with resistance to
fluid flow through the openings.

13. The fluid condition and level sensor and reservoir of claim 12 in
further combination with a controller operatively connected to the coil,
wherein the fluid condition and level sensor is connected to the
reservoir with the sensor configured to be at least partially immersed in
fluid at a predetermined first fluid level, and with the second opening
lower in the reservoir than the first opening such that armature travel
time is correlated by the controller with the predetermined first fluid
level when fluid in the reservoir is above the first opening, and with a
second fluid level lower than the first fluid level when fluid in the
reservoir is below the second opening.

14. The fluid condition and level sensor and reservoir in combination with
the controller of claim 13, wherein the first fluid level corresponds
with a static fluid level in which the fluid in the reservoir is not in
use, and the second fluid level corresponds with a dynamic fluid level in
which the fluid is in use.

Description:

TECHNICAL FIELD

[0001]The present invention relates to fluid level sensors, such as an oil
level sensor in an automotive engine.

BACKGROUND OF THE INVENTION

[0002]Monitoring fluid levels is important in a wide variety of systems
and mechanisms. For example, in many fluid systems, fluid level in a
reservoir achieves a static level when the fluid is not in use, and a
dynamic level lower than the static level when in use, such as when it is
cycled through a system by a pump. Maintaining appropriate static and
dynamic levels may be important to system efficiency and function. In one
such system, an automotive engine, regular oil changes are necessary for
proper maintenance. An oil level sensor may be incorporated into the
vehicle to alert the driver when oil needs to be added.

SUMMARY OF THE INVENTION

[0003]A fluid condition and level sensor is provided that includes a
solenoid body and a coil within the solenoid body. An armature is
surrounded by the coil. The solenoid body defines an armature chamber in
which the armature is movable in response to energizing of the coil. In a
fluid condition and level sensing system, the coil is operatively
connected to a controller which can determine at least one of fluid
temperature, fluid viscosity, fluid level, and a fluid change occurrence.
The sensor may be mounted to a fluid-containing reservoir such that a
first portion of the solenoid body extends into a cavity defined by the
reservoir. The sensor may be positioned so that movement of the armature
is substantially transverse to a direction of fluid level change in the
reservoir. The first portion of the solenoid body within the cavity
defines an opening permitting fluid communication between the cavity and
the armature chamber, such that movement of the armature within the
armature chamber is affected by fluid level in the reservoir.

[0004]The sensor may be referred to as an integrated fluid condition and
level sensor as multiple sensing functions may be integrated into one
sensor. The sensor may be used in many different applications where there
is a need to measure fluid level, fluid viscosity and/or fluid
temperature, such as in engines, transmissions, differentials, food
processing, stationary press oil gear boxes, and fluid cooling systems.

[0005]In some embodiments, the solenoid body defines a second opening,
with the first and second openings arranged to permit fluid communication
between fluid in the reservoir and the armature chamber at respective
opposing sides of the armature and at different levels within the
reservoir. Travel time of the armature in the armature chamber
corresponds to the resistance to fluid flow through the openings. The
"fluid flow" through each respective opening may be air, a liquid, such
as oil, or a combination of both, and depends upon the fluid level (i.e.,
liquid level) in the reservoir.

[0006]For example, if liquid level is low, air, rather than liquid, will
be drawn into the armature chamber. Because air flows much more freely
than liquid, the average armature travel time, also referred to as
response time, will be shorter when liquid level is low. Thus, the "fluid
flow" within the chamber and through the openings discussed herein may be
either air or a liquid, depending on liquid level in the reservoir.

[0007]The above features and advantages and other features and advantages
of the present invention are readily apparent from the following detailed
description of the best modes for carrying out the invention when taken
in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008]FIG. 1 is a schematic cross-sectional illustration of a first
embodiment of an a fluid condition and level sensing system including an
fluid condition and level sensor mounted to a fluid-containing reservoir
shown in fragmentary cross-sectional view;

[0009]FIG. 2 is a schematic cross-sectional illustration of a second
embodiment of a fluid condition and level sensing system including a
fluid condition and level sensor; and

[0010]FIG. 3 is a schematic perspective illustration in exploded view of
the fluid condition and level sensor of FIG. 2.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011]Referring to the drawings, wherein like reference numbers refer to
like components, FIG. 1 shows a fluid condition and level sensing system
10 including a fluid condition and level sensor 12 extending through a
side wall 14 of a fluid reservoir 15. The fluid reservoir 15 may be an
oil pan in an engine, or a transmission, may be a differential, a food
processing container, or any fluid reservoir. The sensor 12 is secured to
the reservoir 15, such as an engine oil pan on a vehicle, so that the
fluid condition and level sensor 12 is positioned in the reservoir 15 to
enable detection of multiple fluid conditions, including fluid
temperature, fluid viscosity, a full fluid level, and a low fluid level,
as further described herein. The fluid condition and level sensor 12 is
operatively connected to an electronic controller 16, which may be
contained either inside or outside of the reservoir 15, such as on a
vehicle engine or elsewhere in the vehicle.

[0012]Referring to FIG. 1, the fluid condition and level sensor 12 has a
solenoid body 20 that includes an outer portion 22, also referred to as a
can, a base portion 24, a coil support portion 26, an extension portion
28 and a cap portion 34. The coil support portion 26 (also referred to as
a bobbin) supports a coil 30. The outer portion 22, base portion 24, coil
support portion 26, extension portion 28, and cap portion 34 may be made
integral or made unitary with one another by casting, molding, or other
processes.

[0013]A pole piece 32 is press-fit or otherwise secured within the outer
portion 22. The cap portion 34 surrounds a distal end of the pole piece
32 and has an electrical connector 36 therethrough operatively connected
to a power source 38, such as a battery, and to the controller 16. Flux
collectors 40 are positioned between the pole piece 32 and the cap
portion 34.

[0014]The base portion 24 and extension portion 28 of the solenoid body
20, along with the pole piece 32, define an armature chamber 42 in which
an armature 44 travels between an end surface 46 of the base portion 24
and an end surface 48 of the pole piece 32. The armature 44 includes a
body portion 50 and a rod portion 52 extending therefrom. A biasing
device, such as spring 53, is positioned between the pole piece 32 and
the armature body portion 50 to bias the armature 44 away from the pole
piece 32 to the unenergized position shown (i.e., the position of the
armature 44 when the coil 30 is not energized).

[0015]A mounting flange 51 secures the sensor 12 through an opening 54 in
the reservoir side wall 14. A bolt or other fastening mechanism (not
shown) extends through mating openings 56, 58 of the flange 51 and the
side wall 14. When secured to the reservoir 15, the base portion 24
extends into a cavity 60 defined by the reservoir 15. The remainder of
the sensor 12 is external to the reservoir 15. The base portion 24 has an
upper opening 62 and a lower opening 64. As used herein, upper opening 62
is referred to as the first opening.

[0016]The armature 44 travels generally transverse to a direction of fluid
level change in the reservoir 15. That is, the armature 44 travels back
and forth in the armature chamber 42 generally transverse (perpendicular)
to the direction of decreasing fluid level (from level A, to level B, to
level C, to level D), or increasing fluid level (from level D, to level
C, to level B, and to level A). The sensor 12 may alternatively be
mounted so that the armature travels at a different angle with respect to
fluid in the reservoir 15.

[0017]The pole piece 32, outer portion 22, coil 30, flux collectors 40,
flange 51 and armature 44 form an electromagnet. Lines of flux are
created in a gap 66 between the pole piece 32 and the armature 44 when
the coil 30 is energized by the electric source 38. When the coil 30 is
energized, the magnetic flux drives the armature 44 toward the pole piece
32, decreasing the portion of the armature chamber 42 between end surface
48 and the armature 44. When energy to the coil 30 ceases, the spring 53
drives the armature 44 back to the unenergized position shown, increasing
the portion of the armature chamber 44 between surface 48 and armature
44. Fluid, whether air or liquid, is pushed through the openings 62, 64
as the armature 44 travels. Fluid in the gap 66 of the armature chamber
42 is also forced through a clearance 67 between the outer diameter of
the armature 44 and the inner diameter of the extension portion 28 as the
armature 44 is cycled. Fluid is similarly forced through channels 69 in
the armature 44. The clearance 67 and channels 69 are configured to be
more resistant to fluid flow than the openings 62, 64. Thus, armature
travel time is a function of the resistance to fluid flow through
clearance 67 and channels 69, which in turn is dependent on whether air
or liquid is present in the chamber 42 and forced through the clearance
67 and channels 69.

[0018]The solenoid valve 20 has a distinctive inductive kick, which is a
distinct dip in current draw followed by an increase in current draw
indicative of the armature 44 reaching the end of travel under known
fluid temperature and fluid fill level. The time period to an inductive
kick after the solenoid valve 20 is energized, is thereby affected by the
resistance to travel encountered by the armature 44.

[0019]The chamber 42, clearance 67, channels 69, and openings 62, 64
described above establish armature travel times indicative of various
fluid conditions such as fluid viscosity and a fluid change occurrence,
as well as various fluid levels in the reservoir 15, as described below.
By tracking the time until inductive kick, and comparing the time with
predetermined times in a look-up table stored on the controller 16, the
controller 16 is able to determine liquid level and viscosity. The sensor
12 is also operable to determine oil temperature based on current.

[0020]Fluid Viscosity

[0021]When the coil 30 is energized and deenergized, the armature 44 moves
within the chamber 42. When the armature 44 moves away from the pole
piece 32, fluid is also pushed through clearance 67 and channels 69 from
chamber 42. By summing the total resistance to fluid flow through the
clearance 67 and channels 69 and friction of the moving parts, this slows
the armature movement such that by measuring the time of armature motion
and then applying an algorithm stored in controller 16, the response time
corresponds to a value indicating the viscosity of the fluid. A higher
fluid viscosity causes the armature 44 to move more slowly as it is
cycled, increasing the armature response time. The inductive "kick" that
occurs at the end of the armature travel in the cycle is detected by the
controller 16, which is connected to coil 30. The thicker the fluid, the
longer it will take for the inductive kick to occur. The total armature
response time is then checked in a look-up table stored in the controller
16 to obtain the relative viscosity of the fluid. Fluid viscosity can
thus be measured using the sensor 12, except when liquid fluid level is
at an extreme low level (i.e., below opening 64, such as at level D).

[0022]The resistance of the sensor 12 may also be measured and the engine
controller voltage controlled to maintain a constant operating current to
the sensor 12 and thus a constant force of the armature 44. This reduces
any effects of current variability on the armature response time.
Limiting the voltage below 12 volts can slow the armature 44 even further
to modify the response time versus viscosity relationship and thereby
increase the sensor sensitivity.

[0023]Fluid Level

[0024]When liquid fluid within the reservoir 15 is above a predetermined
full level B, such as at level A, armature travel time is a function of
the sum of the resistances to fluid travel through the clearance 67 and
the channels 69, with viscous drag on the armature 44 also having a
slight effect. The openings 62, 64 are sized large enough to permit fluid
flow therethrough relatively freely, so that flow through the clearance
67 and channels 69 determines armature travel time. Because these
resistances will vary as liquid fluid level varies, the fluid condition
system 10 can monitor and record liquid fluid level within the reservoir
15, recognizing the instant current liquid level as being within one of
two ranges: above a first level (full level B), and below a second level
(low level C. This information can be conveyed to a system operator, such
as a vehicle driver, if desired, by connecting a display monitor, such as
on an instrument panel screen, to the controller 16 and programming the
controller 16 to send a display signal to the monitor corresponding to
the monitored fluid level.

[0025]If liquid level in the pan 15 is at any level below the opening 64
(i.e., below level C), as indicated by "excessive low" fluid level D in
FIG. 1, any fluid in the chamber 42 is forced out of openings 62, 64 on
the first armature cycle. When the armature 44 cycles, air is drawn into
the chamber 42 instead of liquid, since the openings 62, 64 are above the
liquid level. On subsequent cycles, because only air is moving through
the openings 62, 64, clearance 67, and channels 69, the armature movement
time is relatively fast. Thus, the controller 16 will recognize such an
armature travel time as indicative of an "excessive low" liquid fluid
level, will store this information, and may be programmed to send a
notification to a display in order to notify the vehicle operator of the
need to add fluid.

[0026]When liquid fluid is at any level above the opening 62 (i.e., above
level B), the chamber 42 will be constantly filled with liquid as the
armature 44 travels, and liquid will be forced through the clearance 67
and channels 69. This will create a unique armature travel time
recognized by the controller 16 as indicative of a full liquid fluid
level, and being a function of the sum of resistances to fluid flow
through clearance 67 and channels 69. The sensor 12 may be mounted to the
reservoir 15 such that level B represents a minimum desired static liquid
level and level C represents a minimum desired dynamic liquid level.

[0027]Fluid Temperature

[0028]The temperature of the coil 30 will be affected by the fluid. To
measure fluid temperature, the coil resistance is measured and then
checked against a temperature look-up table stored within the controller
to determine the temperature of the fluid. Alternatively, the sensor 12
may be cycled with a predefined voltage. By measuring the current, the
coil resistance can be calculated and then correlated with temperature.

Second Embodiment

[0029]Referring to FIG. 2, another embodiment of a fluid condition and
level sensing system 110 including a fluid condition and level sensor 112
extending through a side wall 114 of a reservoir 115. The sensor 112 is
secured the reservoir 115, such as an engine oil pan on a vehicle, so
that the fluid condition and level sensor 112 is positioned in the
reservoir 115 to enable detection of multiple fluid conditions, including
fluid temperature, fluid viscosity, and multiple fluid levels, as further
described herein. The fluid condition and level sensor 112 is operatively
connected to an electronic controller 116, which may be contained either
inside or outside of the reservoir 115, such as on a vehicle engine or
elsewhere in the vehicle.

[0030]Referring to FIG. 2, the fluid condition and level sensor 112 has a
solenoid body 120 that includes an outer portion 122, also referred to as
a can, a base portion 124, a coil support portion 126, and a cap portion
134. The coil support portion 126 (also referred to as a bobbin) supports
a coil 130. The outer portion 122, base portion 124, coil support portion
126, and cap portion 134 may be made integral or made unitary with one
another by casting, molding, or other processes.

[0031]A pole piece 132 is press-fit or otherwise secured within the outer
portion 122. The cap portion 134 surrounds a distal end of the pole piece
132 and has an electrical connector 136 therethrough operatively
connected to a power source 138, such as a battery, and to the controller
116. Flux collectors 140 are positioned between the pole piece 132 and
the cap portion 134. A washer 141 is positioned between the coil support
portion 126 and the base portion 124.

[0032]The base portion 124 of the solenoid body 120, along with the pole
piece 132, define an armature chamber 142 in which an armature 144
travels between an unenergized position shown (near an end surface 146 of
the base portion 124) and an energized position (closer to an end surface
148 of the pole piece 132). A biasing device, such as spring 153, is
positioned between the pole piece 132 and the armature 144 to bias the
armature 144 away from the pole piece 132 to the unenergized position
shown (i.e., the position of the armature 144 when the coil 130 is not
energized).

[0033]A mounting flange (not shown) secures the sensor 112 through an
opening 154 in the reservoir side wall 114. A bolt or other fastening
mechanism (not shown) extends through mating openings of the flange and
the side wall 114. When secured to the reservoir 115, the base portion
124 extends into a cavity 160 defined by the reservoir 115. The remainder
of the sensor 112 is external to the reservoir 115.

[0034]The base portion 124 has an extension 161 with an upper opening 162
and a lower opening 164. As used herein, upper opening 162 is referred to
as the first opening. As best shown in FIG. 3, the lower opening 164
extends axially and is in communication with a radial slot 165.

[0035]In this embodiment, the armature 144 travels generally transverse to
a direction of fluid level change in the reservoir 115. That is, the
armature 144 travels back and forth in the armature chamber 142 generally
transverse (perpendicular) to the direction of decreasing liquid fluid
level from level AA, to level BB to level CC, to level DD, or increasing
liquid fluid level change from level DD, to level CC, to level BB, and to
level AA. The sensor may alternatively be positioned so that the armature
travels at other angles with respect to the fluid level.

[0036]The pole piece 132, outer portion 122, coil 130, flux collectors
140, washer 141 and armature 144 form an electromagnet. Magnetic flux is
created when the coil 130 is energized by the electric source 138. The
magnetic flux drives the armature 144 toward the pole piece 132,
increasing the portion of the armature chamber 142 between end surface
146 and the side 145 of the armature 144. When energy to the coil 130
ceases, the spring 153 drives the armature 144 back to the unenergized
position shown, decreasing the portion of the armature chamber 142
between surface 146 and armature 144. Fluid, whether air or liquid, such
as oil, is pushed through the openings 162, 164 as the armature 144
travels. Opening 162 communicates air or liquid with the chamber 142 at a
first side 145 of the armature 144. Opening 164 communicates air or
liquid within the reservoir 115 below level DD with a second side 147 of
the armature 144. Air can be communicated between the portions of the
chamber 142 at the two sides 145, 147 of the armature 144 through a
clearance 166 between the inner diameter of the cavity forming the
chamber 142, and the outer diameter of the armature 144. The clearance
166 is designed to inhibit any communication of liquid therethrough.
Thus, armature travel time is a function of the resistance to fluid flow
through the openings 162, 164, which in turn is dependent on whether air
or liquid is flowing through the openings. The time period to an
inductive kick after the solenoid 112 is energized, is thereby affected
by the resistance to fluid flow through the openings 162, 164. The
chamber 142 and openings 162, 164 described above establish armature
travel times indicative of various fluid conditions such as fluid
viscosity and a fluid change occurrence, as well as various fluid levels
in the reservoir 115, as described below. By tracking the time until
inductive kick, and comparing the time with predetermined times in a
look-up table stored on the controller 116, the controller 116 is able to
determine liquid fluid level and viscosity. The sensor 112 is also
operable to determine fluid temperature based on current.

[0037]Fluid Viscosity

[0038]When the coil 130 is cycled (energized and deenergized), the
armature 144 moves back and forth within the chamber 142. When the coil
130 is energized and deenergized, the armature 144 moves toward and away
from the pole piece 132, respectively, and fluid is pushed through
openings 162, 164 from chamber 142. The total resistance to fluid flow of
the openings 162, 164 and friction of the moving parts slows the armature
movement such that by measuring the time of armature motion and then
applying an algorithm stored in the controller 116, the response time
corresponds to a value indicating the viscosity of the fluid. A higher
fluid viscosity causes the armature 144 to move more slowly as it is
cycled, increasing the armature response time. The inductive "kick" that
occurs at the end of the armature travel toward the pole piece 132 is
detected by the controller 116, which is connected to coil 130. The
thicker the fluid, the longer it will take for the inductive kick to
occur. The total armature response time is then checked in a look-up
table stored in the controller 116 to obtain the relative viscosity of
the fluid. Fluid viscosity can thus be measured using the sensor 112
(except when fluid is at an extreme low level (i.e., below opening 164,
such as at level D)).

[0039]The resistance of the sensor 112 may also be measured and the engine
controller voltage controlled to maintain a constant operating current to
the sensor 112 and thus a constant force of the armature 144. This
reduces any effects of current variability on the armature response time.
Limiting the voltage below 12 volts can slow the armature 144 even
further to modify the response time versus viscosity relationship and
thereby increase the sensor sensitivity.

[0040]Fluid Level

[0041]When liquid within the reservoir 115 is above a predetermined full
level AA, armature travel time is a function of the sum of the
resistances to fluid travel through each of the openings 162, 164, with
viscous drag on the armature 144 also having a slight effect. Because
these resistances will vary as liquid fluid level varies, the fluid
condition system 110 can monitor and record fluid level within the
reservoir 115, recognizing the current liquid fluid level as being within
one of three ranges: above level AA (e.g., an overfill level), below
level DD (e.g., a low level), and between level AA and level DD (e.g., a
full level). This information can be conveyed to a vehicle operator, if
desired, by connecting a display monitor, such as on an instrument panel
screen, to the controller 116 and programming the controller 116 to send
a display signal to the monitor corresponding to the monitored liquid
fluid level.

[0042]If fluid level in the reservoir 115 is at any level below the
opening 164, (i.e., any level below level DD in FIG. 1), any liquid fluid
in the chamber 42 is forced out on the first armature cycle. When the
armature 144 cycles, air is drawn into the chamber 42 instead of liquid,
since the openings 162, 164 are above the liquid fluid level. On
subsequent cycles, because only air is moving through the openings 162,
164, the armature movement time is relatively fast. Thus, the controller
116 will recognize such an armature travel time as indicative of an
"excessive low" liquid fluid level, will store this information, and may
be programmed to send to a display a notification to the system operator
of the need to add oil.

[0043]If liquid fluid level in the pan 115 is at any level below the
opening 162, but above the opening 164 (i.e., a level between level AA
and level DD, such as level BB and level CC, the armature 144 will
displace at least some liquid fluid out of the chamber 142 on the first
armature cycle. When the spring 153 biases the armature 144, opening 164
will draw in fluid. Because opening 162 is above the liquid fluid level,
and at least some of the chamber 142 is above liquid fluid level, some
air will be drawn into the chamber 142 when the sensor 112 is energized.
Therefore, the armature movement time will be slower than when liquid
fluid is at the extreme low level DD, but not as slow as when fluid level
is above opening 162. The controller 116 will compare the armature
movement time to stored values and recognize such an armature travel time
as indicative of a level between level AA and level DD.

[0044]When liquid fluid is at any level above the opening 162, such as
above level AA, the chamber 142 will be constantly filled with liquid
fluid as the armature 144 travels, and liquid will be forced through
openings 162, 164. This will create a unique armature travel time
recognized by the controller 16 such as indicative of an overfill level,
depending on the mounted position of the sensor 112 within the reservoir
115, and being a function of the sum of resistances to fluid flow through
openings 162, 164.

[0045]Fluid Temperature

[0046]The temperature of the coil 130 will be affected by the fluid. To
measure fluid temperature, the coil resistance is measured and then
checked against a temperature look-up table stored within the controller
to determine the temperature of the fluid. Alternatively, the sensor 112
may be cycled with a predefined voltage. By measuring the current, the
coil resistance can be calculated and then correlated with temperature.

[0047]While the best modes for carrying out the invention have been
described in detail, those familiar with the art to which this invention
relates will recognize various alternative designs and embodiments for
practicing the invention within the scope of the appended claims.